The morphological and biochemical studies proposed will describe the embryonic development of a group of adrenergic neurons in the rat brain stem. An interdisciplinary approach using immunocytochemistry, atuoradiography, radioenzymatic assay and high performance liquid chromatography will be applied to follow the initial appearance and developmental profile of neurotransmitter markers characterizing the adrenergic phenotype in central neurons. These techniques have been previously applied by this investigator to study the development of adrenergic cells in the peripheral nervous system. Specifically, the proposed studies seek to a) document the initial expression of adrenergic enzymes in the embroynic medulla oblongata, b) describe the prenatal biochemical development of central adrenergic neurons, c) define the neurogenesis of antigenically characterized neurons, d) compare centrla to peripheral adrenergic cells with respect to neurotransmitter phenotypic expressions, development and possible regulation by glucocorticoids, and e) elucidate possibe transplacental effects of maternal hormones on adrenergic development in the fetal brain. More generally, these studies address current issues in cell biology, embryology and neuroscience concerning processes involved in cell determination and cell differentiation. By studying neurotransmitter phenotypic expression in the brain of the rat embryo and characterizing the role of fetal and maternal endocrine factors as extracellular influences, these studies promise to elucidate loci where changes in the milieu of the developing neuron may lead to abnormal neuronal development. Such knowledge may contribute to our understanding of birth defects in the human and ultimately lead to therapeutic approaches for the correction of neuronal deficits.